High-performance liquid chromatography (HPLC) instruments are analytical tools for separating, identifying, and quantifying compounds. In a typical liquid chromatography analysis, a pump takes in and delivers a mixture of liquid solvents to a sample manager, where the material under analysis, called the sample, awaits injection into the solvents. The sample is the material under analysis. Examples of samples include complex mixtures of proteins, protein precursors, protein fragments, reaction products, and other compounds, to list but a few. The mobile phase, comprised of a sample dissolved in a mixture of solvents, moves to a point of use, such as a column, referred to as the stationary phase. By passing the mobile phase through the column, the various components in the sample separate from each other at different rates and thus elute from the column at different times.
The separation techniques of a liquid chromatography (LC) system are often used in combination with one or more additional analysis techniques to produce multidimensional information about a sample. For example, mass spectrometry (MS) can provide molecular weight and structural information. A difficulty associated with combining disparate techniques occurs at the interface between the techniques. For example, the combination of liquid chromatography and mass spectrometry requires effective transport of the sample eluent produced by the liquid chromatography system to the mass spectrometry instrument for analysis. Industry has devised various ionization techniques to achieve this sample eluent transport, including field desorption, thermospray, and electrospray. When used in conjunction with liquid chromatography techniques, many consider electrospray (ESI) to be the ionization method of choice. For electrospray ionization, a union couples the liquid chromatography column to an ESI emitter. A clogged or poorly performing ESI emitter, however, will produce poor data quality and will reduce the productivity of the LC-MS system until the ESI emitter is replaced.